There are numerous requirements for flexible hoses having preformed shapes. For example, in various automotive and other types of vehicles employing liquid cooled engines, it is customary to interconnect the engine with a radiator by a flexible radiator hose. Frequently it is desirable for the hose to be fabricated into preformed shapes to accommodate the spatial requirements. At the present time there are two basic ways of forming such hoses.
In the first method an uncured hose is formed from a organic rubber or similar elastomers and a knitted reinforcing layer. A layer of the elastomer is disposed around a mandrel. Following this the knitted reinforcement is placed around the elastomeric layer. This may be accomplished by slipping a knitted sleeve over the mandrel or knitting the sleeve directly therearound. The sleeve is usually knitted with a lock stitch which allows it to be easily stretched and deformed into numerous shapes. Next a second layer of the elastomer is disposed around the knitted reinforcement. The uncured hose is then cured on the mandrel whereby it acquires a permanent shape corresponding to the shape of the mandrel.
After the curing process, the individual hoses are removed from the mandrels by sliding them off. Due to the reinforcement being a knitted sleeve, the hose has a sufficient stretch and flexibility to allow it to be slipped from the mandrel. However, due to the characteristics of the knitted reinforcement, a hose of this type has numerous undesirable limitations and objections. The hose has a limited ability to withstand an internal pressure as it tends to balloon when the pressure rises. This means the hose must operate at relatively low pressures. In addition, although the hose is flexible, there is a considerable amount of internal working when the hose is distorted. As a consequence, the hose cannot withstand continuous flexing as the various layers of elastomer and/or the knitted sleeve tend to separate. Also, the hose is subjected to being easily punctured with sharp hand tools such as screw drivers, etc.
The second method provides a hose which is reinforced by a fabric. The hose is formed by wrapping a layer of an uncured elastomer around a contoured mandrel. Next a woven fabric sleeve is wrapped around the elastomer. Following this, an outer layer of the elastomer is wrapped around the fabric. This assembly is then heated until the elastomer is fully cured. The hose is then removed from the mandrel. The use of a woven reinforcement does tend to increase the amount of pressure that the hose can withstand. However, the finished hose still has numerous disadvantages. First of all, since the fabric is woven it will not stretch easily. This makes it very difficult, if not impossible, to form the fabric around sharp bends without causing it to pucker, etc. Moveover, it is frequently very difficult to remove the fully cured hose from the mandrel unless the mandrel can be taken apart of disassembled or else is of an expendable nature that is only used and then destroyed. Moreover, a large amount of hand labor is required to lay up the hose. This, of course, greatly increases the cost of the hose. In addition, the hose is still subjected to internal working and premature failure through excessive flexing.